Fix notification row transparency.

Bug: 400307362
Fixes: 400307362
Test: Create notifications that are colorized, non-colorized, HUNs,
custom views. Lock / unlock device. Make sure transparency looks
correct.
Flag: com.android.systemui.notification_row_transparency

Change-Id: I9c1891828689cd0bb239fb7c18f0ebd8b1721e99